The invention relates to a method of extracting coal in a longwall working in which the coal is obtained at the longwall face, is loaded and is removed with the aid of a continuous conveyor, acting as a longwall-heading or face conveyor, into one of two subsidiary galleries. In addition, the invention relates to worm conveyor to carry out such a method.
Such methods of extracting coal are applicable to level and to inclined stratifications, because in such stratification conditions gravity is not adequate to remove the coal and hence the heading conveyor has to be employed as a continuous conveyor. A continuous conveyor is required for the continuous removal of the coal because it is only by such means that it is possible to achieve a narrow space which accommodates the conveyor and enables securing of the roof. The length of the longwall face extending between the two subsidiary galleries is basically optional; it may run to several hundred meters, but if residual pillars are left, upon the pulling-in of a spur of coal, for instance for the driving forward of heading packs, and in other special cases it can become reduced to substantially smaller lengths. Subsidiary galleries are therefore also typified by subsidiary spaces involved at the end of the longwall and, for example, ventilated by air outlets.
The extraction methods indicated in the foregoing are in themselves already known. The coal is obtained, loaded and removed principally by mechanical means. Mechanical coal extraction proceeds by machine, mostly with a slicing or cutting action and hence with an essentially point-by-point attack on the longwall face, bearing in mind its length. However with the cutting type of extraction, the extraction machine as a rule also performs the loading work. With the slicing type of extraction an additional loading operation is required, mostly with the aid of a further machine. By way of face conveyors, chain scraper conveyors are almost exclusively employed because the bottom-channel run of such conveyors is sufficiently resistant and can therefore be utilized as a track for the machines employed in the longwall heading.
The essentially point-by-point attack along the longwall face is unfavourable because the extraction rate is dependent solely on the width of the extraction machine, which determines the depth of penetration into the body of coal, and on the speed of advance of the machine. Therefore increase in the extraction rate demands correspondingly increased installed performance of the extraction machine. The power demand of chain scraper conveyors is also unusually high because such conveyors are energy-wise unfavourable due to friction between the chain belt and the channels.
At the basis of the invention is the object of extending the extraction, loading and removal of the debris in the heading to the entire longwall face and, in so doing, to make the chain scraper conveyor superfluous as a track for an extraction machine.